Most hydraulic steering systems for machines use a variable position control valve operatively connected to a steering wheel for varying flow rate of hydraulic fluid from a hydraulic pump to one or more hydraulic steer cylinders. The rate of fluid flow and thus the steering speed is proportional to the rotational position of the steering wheel. The steering control valve on some machines are closed center valves connected to a load sensing or load responsive hydraulic pump which automatically upstrokes to meet the demand for fluid when the steering control valve is opened to communicate the pump with the steer cylinders.
One of the problems with such systems is that changing the displacement of the pump tends to lag behind movement of the steering control valve to a steer position and generally either overshoots or undershoots the target flow rate established by the area opening of the steering control valve.
Thus it would be desirable to provide an electrohydraulic steering system having fast response to minimize lag time between the operator steer input command and actual steering of the machine and which minimizes overshoot and undershoot of the target flow rate established by the input command